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12/02/09

Seek new dimensions of excitement. Achieve superior cornering performance. The key to superior cornering performance is an optimal balance of front and rear weight distribution and a shortened wheel base.

Yamaha’s compact in-line four-cylinder engine provides this advantage for the entire YZF-R series. The in-line four-cylinder engine offers a new dimension in linear throttle action. This is achieved through the crossplane crankshaft and the 90 degrees space positioning of its four crank pins. The rider operates the throttle producing torque. This torque is essentially produced solely from engine combustion. However, total engine output or composite torque is actually a combination of this combustion torque plus the inertial torque produced by the rotation of the crankshaft.

Inertial torque is unlike combustion torque. Inertial torque is resulting from the rotation of the crankshaft. Combustion torque can be operated by the rider through the throttle. But inertial torque grows larger in proportion to the speed of the crankshaft rotation and thus prevents linear throttle action from being achieved. As you can see this is due to the crank moving the fastest at top and bottom dead center and the slowest at 90 degrees and 270 degrees. The result is this graph. The rider wants combustion torque but because of the addition of inertial torque which cannot be controlled the result is something disordered, a composite torque unlike combustion torque. The solution to this is found in the crossplane crankshaft. By differing the adjacent cranks’ rotations by 90 degrees inertial torque fluctuation is eliminated. As you can see, inertial torque is almost completely eliminated and the combustion torque sought by the rider is almost perfectly matched by the composite torque of the engine. In other words, the rider is able to achieve linear power delivery and traction through the operation of the throttle.

With the exception of a few racing machines, no other commercially available motorcycle has offered an in-line four-cylinder engine with a crossplane crankshaft. This new dimension in linear throttle action brought about through Yamaha technology is going to shift the entire paradigm of the super sports motorcycle world.